It is really quite bad, enough for me to get out of the seat and cringe.
Tried new pads – still judders.
All rotors and fixings are tight, should I try copper slip behind the old pads? Or have you had and solved this another way?
Welds all fine, (I realise these have a small history of going around that area)

i had this on a faux bar Ventana, turns out the lower seatstay had ovalised around the bearing, vibrated like a sybian

No pivots to worry about. Should I google sybian?

try a different wheel, if its ok its the wheel bearings in your hub if not it may be a sticky piston or a wonky mount or even worse a wonky frame

Also had a similar judder on my Hopes, turned out to be the effectively wavey pattern of the rotor, swapped to a round Shimano one and the judder went.

vibrated like a sybian

DO NOT google this 😉

Try securing the hose more, Mine used to do the same thing on the back of my hummer, few more zip ties to stop the hose moving about cured it.

sounds like a bent rotor or disc contamination to me?